diff --git a/frontend/src/api/types.ts b/frontend/src/api/types.ts
index 1915d60c75..8a5c5b7e72 100644
--- a/frontend/src/api/types.ts
+++ b/frontend/src/api/types.ts
@@ -2,13 +2,16 @@ import type { AnyObject } from '@mtes-mct/monitor-ui'
 
 // Don't forget to mirror any update here in the backend enum.
 export enum ApiErrorCode {
+  EXISTING_MISSION_ACTION = 'EXISTING_MISSION_ACTION',
   /** Thrown when attempting to delete an entity which has  to non-archived children. */
   FOREIGN_KEY_CONSTRAINT = 'FOREIGN_KEY_CONSTRAINT',
+
   /** Thrown when attempting to archive an entity linked to non-archived children. */
   UNARCHIVED_CHILD = 'UNARCHIVED_CHILD'
 }
 
 export interface BackendApiErrorResponse {
+  code: ApiErrorCode | null
   type: ApiErrorCode | null
 }
 
diff --git a/frontend/src/features/Mission/components/MissionForm/index.tsx b/frontend/src/features/Mission/components/MissionForm/index.tsx
index b4ed249055..abe765cff7 100644
--- a/frontend/src/features/Mission/components/MissionForm/index.tsx
+++ b/frontend/src/features/Mission/components/MissionForm/index.tsx
@@ -617,8 +617,11 @@ export function MissionForm() {
           </div>
           <div>
             <MissionInfos>
-              {mainFormValues.createdAtUtc && (
-                <>Mission créée le {customDayjs(mainFormValues.createdAtUtc).utc().format('D MMM YYYY, HH:mm')}. </>
+              {mainFormValues.createdAtUtc && mainFormValues.missionSource && (
+                <>
+                  Mission créée par le {Mission.MissionSourceLabel[mainFormValues.missionSource]} le{' '}
+                  {customDayjs(mainFormValues.createdAtUtc).utc().format('DD/MM/YYYY à HH:mm')}.{' '}
+                </>
               )}
               {!mainFormValues.createdAtUtc && <>Mission non enregistrée. </>}
               {mainFormValues.updatedAtUtc && (
@@ -692,6 +695,7 @@ export function MissionForm() {
 
 const MissionInfos = styled.div`
   font-style: italic;
+  color: ${p => p.theme.color.slateGray};
 `
 
 export const BackToListIcon = styled(Icon.Chevron)`